The use of microfluidic systems for the acquisition of chemical and biological information is becoming increasingly more important due to a number of considerations. For example, complicated biochemical reactions, when conducted in microfluidic volumes, may be carried out using very small volumes of liquid. As the volume of a particular liquid needed for such testing regimes is small, often on the order of nanoliters, the amounts of reagents and analytes used can be greatly reduced. Reduction in the amounts of reagents and analytes can greatly reduce the costs associated with microfluidic testing compared with conventional testing systems.
In addition, the response time of reactions is often much faster in microfluidic systems, leading to a decrease in the overall time required for a particular testing regime. Also, when volatile or hazardous materials are used or generated during testing, performing reactions in microfluidic volumes can increase the safety of a testing regime and can also reduce the quantities of hazardous materials that require specialized disposal after testing is completed.
In addition, microfluidic testing systems generally require much less bulky equipment than conventional testing systems, enabling use of microfluidic testing systems in mobile or residential settings. Microfluidic testing systems can thus be used in settings that conventionally required the sampling of fluids at one location and testing of the fluids at another location.
While microfluidic testing is increasing in popularity, the technology associated with microfluidic testing remains problematic in a number of areas. In particular, it has been found that sample preparation of various bodily fluids has been difficult to accomplish on a microfluidic level. For example, the analysis of blood often requires the removal of erythrocytes (red blood cells) for accurate testing. This has generally been accomplished by centrifugating a blood sample to separate the red blood cells from the remainder of the blood sample. Similar separation techniques have also been necessary to test saliva samples.
The small-scale nature of microfluidic testing systems has to date proved problematic when dealing with test samples that must be centrifugated prior to testing, with no known microfluidic centrifugation systems having been successfully developed. Due to this limitation in conventional microfluidic systems, centrifugation of samples to be tested has generally been accomplished with conventional, full-scale centrifugation devices after which a small (e.g., microfluidic) volume of the sample to be tested has been transferred to a microfluidic test coupon for further manipulation and analysis.
Accordingly, while it is desired to use microfluidic test systems in a wide range of applications, the limitations inherent in centrifugating liquids at the microfluidic level remain problematic.